Secondary battery

Abstract

To provide a secondary battery capable of suppressing movement of the electrode stack inside the exterior member without affecting the surface treatment normally performed on the electrode stack.SOLUTION: A secondary battery 10 includes: an electrode module 20 that includes an electrode stack 21, which is a stack of multiple positive electrode layers 27 and negative electrode layers 28, each stacked via a separator 24; an exterior material 30 that encases the electrode module 20; and a metallic material 50 that is placed between the electrode module 20 and the exterior material 30 with higher surface hardness and larger surface roughness. The electrode stack 21 of the electrode module 20 has an outer surface at both ends of the stacking direction D and an inner surface of the exterior material 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] Patent Document 1 discloses an electrode module in which the relationship μeff<μ1 exists between the effective static friction coefficient μeff between the outermost layer of the electrode laminate and the inner layer of the laminate film exterior member and the larger of the static friction coefficient μ1 between the positive electrode and separator and the static friction coefficient between the negative electrode and separator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 034350 Summary of the Invention [Problem to be solved by the invention]

[0004] By adjusting the effective static friction coefficient μeff between the outermost layer of the electrode laminate and the inner layer of the laminate film packaging member to a predetermined value, it is possible to suppress damage to the laminate film packaging member due to vibration of the electrode laminate. However, when the outermost layer of the electrode laminate is made of, for example, aluminum (Al), treating the Al surface to increase the friction coefficient may have some effect on the corrosion prevention treatment and treatment to improve the seal strength that are usually required for the Al surface, leaving room for improvement.

[0005] In consideration of the above, an object of the present invention is to provide a secondary battery that can suppress the movement of an electrode stack within an exterior member without affecting the surface treatment that is normally performed on the electrode stack. [Means for solving the problem]

[0006] The secondary battery according to the present invention as set forth in claim 1 comprises an electrode module including an electrode stack in which a plurality of positive electrode layers and negative electrode layers are stacked with separators interposed therebetween, an exterior member that wraps the electrode module, and a metal member that is disposed between the electrode module and the exterior member and has a higher surface hardness and a greater surface roughness than outer surfaces of the electrode stack at both ends in the stacking direction of the electrode module and the inner surface of the exterior member.

[0007] In the secondary battery according to the first aspect of the present invention, a metal member having a higher surface hardness and a larger surface roughness than the outer surfaces of the electrode module's electrode stack at both ends in the stacking direction and the inner surface of the outer casing is disposed between the electrode module and the outer casing. Therefore, the irregularities on the surface of the metal member penetrate into the outer surface of the electrode module and the inner surface of the outer casing, respectively, thereby increasing the frictional force at the contact surface with the metal member compared to when the metal member is not interposed. This makes it possible to suppress movement of the electrode module within the outer casing. Furthermore, because the outer surface of the electrode module is not treated, there is no effect on the surface treatment typically applied to the electrode module.

[0008] The secondary battery according to the present invention as set forth in claim 2 is configured as set forth in claim 1, wherein the electrode stack is configured by stacking a plurality of bipolar electrodes, each bipolar electrode having the positive electrode layer formed on one side of a current collector and the negative electrode layer formed on the other side, with the separator interposed therebetween, and the electrode module includes end current collectors stacked on both ends of the electrode stack in the stacking direction.

[0009] In conventional electrode modules having bipolar electrodes, for example, when the end current collector is made of aluminum, the aluminum surface, which is the outer surface of the end current collector, is subjected to corrosion prevention treatment or treatment to improve sealing strength. Unlike electrode modules having a general electrode laminate, electrode modules having bipolar electrodes require increased friction between the electrode module and the exterior member while ensuring the current-carrying function of the main surfaces of the end current collector. For example, in electrode modules having bipolar electrodes, treatment to increase friction, such as the use of a resin adhesive, may have some effect on the treatment applied to the aluminum surface.

[0010] In the secondary battery according to the present invention, the electrode stack is configured by stacking a plurality of bipolar electrodes with separators interposed therebetween, and the electrode module includes end current collectors stacked on both ends of the electrode stack in the stacking direction. Therefore, the metal member disposed between the electrode module and the exterior member can increase the frictional force between the outer surface of the end current collector and the inner surface of the exterior member and the surface of the metal member. This makes it possible to suppress movement of the electrode module within the exterior member without impairing the current-carrying function of the main plane of the end current collector.

[0011] A secondary battery according to the present invention as set forth in claim 3 has the configuration as set forth in claim 2, wherein the metal member is disposed between at least a part of the end current collector and the exterior member.

[0012] In the secondary battery according to the present invention, the metal member is disposed between at least a portion of the end current collector and the exterior member, so that when the metal member is disposed on only a portion of the outer surface of the end current collector, the cost required for the metal member can be reduced. Also, when the metal member is disposed on the entire outer surface of the end current collector, movement of the electrode module within the exterior member can be more effectively suppressed.

[0013] The secondary battery of the present invention described in claim 4 has the configuration described in any one of claims 1 to 3, in which the exterior member is a laminate film formed by overlapping film materials, and the inner film on the electrode module side of the laminate film and the outer surfaces of both ends in the stacking direction of the electrode stack are made of the same material.

[0014] In the secondary battery according to the fourth aspect of the present invention, the inner film on the electrode module side of the laminate film forming the exterior member and the outer surfaces of both ends in the stacking direction of the electrode laminate are made of the same material, but a metal member is provided between the inner film and the outer surface, which has a higher surface hardness and a larger surface roughness than the outer surface and the inner film. Therefore, the unevenness of the surface of the metal member bites into the outer surface and the inner film on the electrode module side of the laminate film, respectively, thereby increasing the frictional force at the contact surface with the surface of the metal member. This makes it possible to suppress movement of the electrode module within the laminate film.

[0015] The secondary battery according to the present invention described in claim 5 has the configuration described in any one of claims 1 to 4, wherein the metal member has a metal foil having a polished layer on its surface and a surface-hardened layer provided on the surface of both ends of the metal foil in the thickness direction.

[0016] In the secondary battery according to the present invention, the metal foil constituting the metal member has a polished layer on its surface, which allows a roughened surface with irregularities to be formed on the surface of the metal foil. Also, the metal member has a surface-hardened layer on its surface, which hardens the irregular surface, making it easier for the irregularities of the metal member to bite into the outer surface of the electrode module and the inner surface of the exterior member. [Effects of the Invention]

[0017] As described above, the secondary battery according to the present invention has the excellent effect of being able to suppress movement of the electrode stack within the exterior member without affecting the surface treatment that is normally performed on the electrode stack. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view in a stacking direction of a secondary battery according to an embodiment of the present invention. [Figure 2] 2 is an explanatory view illustrating a molding process of an exterior member of the secondary battery of FIG. 1. FIG. [Figure 3] 1. FIG. 4 is an explanatory view illustrating a process of assembling an exterior member of the secondary battery of FIG. [Figure 4] FIG. 2 is an enlarged cross-sectional view of a main part including the high-friction shim of FIG. 1. [Figure 5] FIG. 1 is a cross-sectional view showing an example of a high-friction shim. [Figure 6] FIG. 10 is a perspective view showing an example of the arrangement of high-friction shims. [Figure 7] FIG. 10 is a perspective view showing another example of the arrangement of high-friction shims. [Figure 8] 1 is a graph showing the measurement results of the static friction coefficient. [Figure 9] FIG. 1 is a cross-sectional view in the stacking direction of a conventional secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0019] A secondary battery 10 according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view in the stacking direction of a secondary battery 10 according to one embodiment of the present invention. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and duplicated explanations are omitted. In the drawings, duplicated reference numerals may be omitted as appropriate. In FIG. 1, the thicknesses and thickness ratios of each component are exaggerated for ease of explanation and may differ from the actual thicknesses.

[0020] The secondary battery 10 of this embodiment is, for example, a bipolar secondary battery, and is used as a battery for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The secondary battery 10 is, for example, a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The secondary battery 10 may also be, for example, an electric double layer capacitor.

[0021] As shown in Fig. 1, the secondary battery 10 includes an electrode module 20 and an exterior member 30 arranged to encase the electrode module 20. The electrode module 20 includes an electrode stack 21 formed by stacking a plurality of bipolar electrodes 22 with separators 24 interposed therebetween, and a seal portion 40 arranged to surround the electrode stack 21. That is, in the electrode stack 21, the separators 24 are interposed between the bipolar electrodes 22 adjacent to each other in the stacking direction D. In this embodiment, as an example, the electrode module 20 has a rectangular shape when viewed from the stacking direction (see Fig. 3).

[0022] The bipolar electrode 22 includes a current collector 26 formed in the shape of a rectangular sheet, a positive electrode layer 27 formed on one surface of the current collector 26, that is, the lower surface in the stacking direction D, and a negative electrode layer 28 formed on the other surface of the current collector 26, that is, the upper surface in the stacking direction D. That is, the bipolar electrode 22 is formed by bonding the positive electrode layer 27 and the negative electrode layer 28 to both surfaces of the current collector 26 and integrating them.

[0023] The current collector 26 is a chemically inactive electrical conductor that continues to pass current through the positive electrode layer 27 and the negative electrode layer 28, for example, during discharging or charging of the secondary battery 10. In this embodiment, the current collector 26 is formed, for example, from a rectangular metal foil (aluminum foil) made of Al. As shown in FIG. 1 , the positive electrode layer 27 and the negative electrode layer 28 are formed inside the periphery of the current collector 26, and the rectangular frame-shaped peripheral portion of the current collector 26 is an uncoated region where the positive electrode layer 27 and the negative electrode layer 28 are not coated.

[0024] The positive electrode layer 27 is formed on the lower surface of the current collector 26, and the negative electrode layer 28 is formed on the upper surface of the current collector 26. Note that the bipolar electrode 22 constituting the lowermost portion of the electrode module 20 in the stacking direction D does not have the positive electrode layer 27 on the lower surface. Also, the bipolar electrode 22 constituting the uppermost portion of the electrode module 20 in the stacking direction D does not have the negative electrode layer 28 on the upper surface.

[0025] That is, in the electrode laminate 21, current collectors 26 are laminated at both ends (ends) in the lamination direction D, and in this embodiment, the current collectors 26 laminated at the ends are referred to as end current collectors 26A.

[0026] In the electrode module 20, the positive electrode layer 27 of one bipolar electrode 22 faces the negative electrode layer 28 of another bipolar electrode 22 adjacent to it on one side in the stacking direction D, with the separator 24 sandwiched between them. In the electrode module 20, the negative electrode layer 28 of one bipolar electrode 22 faces the positive electrode 18 of another bipolar electrode 22 adjacent to it on the other side in the stacking direction D, with the separator 24 sandwiched between them.

[0027] The separator 24 is disposed between adjacent bipolar electrodes 22 in the stacking direction D, and is interposed between the positive electrode layer 27 and the negative electrode layer 28. By isolating the positive electrode layer 27 and the negative electrode layer 28, the separator 24 prevents short circuits due to contact between adjacent electrode layers while allowing charge carriers such as lithium ions to pass through. The separator 24 is formed, for example, in a sheet shape, but is not limited to a sheet shape and may be in a bag shape.

[0028] The seal portion 40 is formed in a frame shape on the peripheral edge of the electrode stack 21 so as to surround the electrode stack 21, and includes a pair of holding seal materials 42, a peripheral holding seal portion 44, and a spacer 46. The pair of holding seal materials 42 are bonded to the peripheral edge of the upper or lower surface of each current collector 26, respectively, and hold each current collector 26 from both sides in the stacking direction D.

[0029] The pair of holding sealing materials 42 are formed, for example, in a two-layer structure by folding one film in two. That is, the peripheral edge side, which is the area not sandwiched between the current collector 26, is a folded portion (bent portion) of the film, and the two holding sealing materials 42 are bonded to each other at this peripheral edge. In addition, at least one of the surfaces of the pair of holding sealing materials 42 opposite to the surfaces facing each other is bonded to the spacer 46.

[0030] In this embodiment, the pair of holding sealing materials 42 is made up of one film, but the present invention is not limited to this, and the pair of holding sealing materials 42 may be made up of two films.

[0031] The outer peripheral holding seal portion 44 holds the outer peripheral portions of the plurality of pairs of holding seal materials 42. Specifically, the outer peripheral holding seal portion 44 is a welding layer formed by integrating the plurality of pairs of holding seal materials 42 and the plurality of spacers 46 described later by welding the portions that overlap in the stacking direction of the plurality of pairs of holding seal materials 42 and the plurality of spacers 46 described later.

[0032] The spacer 46 is interposed between two pairs of holding sealing materials 42 adjacent to each other in the stacking direction D. The spacer 46 maintains a gap between the pair of holding sealing materials 42 adjacent to each other in the stacking direction D.

[0033] The spacer 46 is formed in a frame shape and is disposed on the peripheral portion 2 of the current collector 26 when viewed from the stacking direction D. In the present embodiment, the peripheral portion of each separator 24 is sandwiched and fixed between the spacer 46 and the lower holding seal material 42 of the pair of holding seal materials 42, for example.

[0034] The sealing portion 40 is formed of, for example, an insulating resin, and examples of the resin constituent material include polypropylene (PP), polyphenylene sulfide (PPS), modified polyphenylene ether (modified PPE), polyethylene (PE), etc. Cover members 16, which will be described later, are disposed on the outside of each of the sealing portions 40 on the short sides of the electrode stack 21.

[0035] In this embodiment, a plurality of spaces are provided within the electrode module 20. Each space is provided between adjacent bipolar electrodes 22 in the stacking direction D with a separator 24 interposed therebetween, and is a space that is airtight and liquid-tight sealed by a seal portion 40. Each space contains an electrolyte solution (not shown) containing, for example, a non-aqueous solvent and a supporting salt. The electrolyte solution is impregnated into the separator 24, the positive electrode layer 27, and the negative electrode layer 28.

[0036] The exterior member 30 is disposed so as to encase the electrode module 20, and is composed of a pair of exterior bodies 31 made of a laminate film formed by overlapping film materials. In this embodiment, the exterior member 30, i.e., the exterior body 31, is composed of, for example, an aluminum laminate film. Here, an example of a method for forming the exterior body 31 will be described. FIG. 2 is an explanatory diagram illustrating the molding process of the exterior body 31 as the exterior member 30 of the secondary battery 10 of FIG. 1. Note that the cross-sectional views taken along line AA in each process in FIG. 2 are depicted as a cross section of one sheet, but actually show a laminate film.

[0037] As shown in FIG. 2(A), first, an aluminum foil 32 having a thickness t of 0.1 mm and a rectangular shape in a plan view is placed as an example of a conductive metal layer. Next, as a sealing process, as shown in FIG. 2(B), a sealant film 34 that provides sealing properties when heated is disposed around the periphery of the aluminum foil 32. As an example, the sealant film 34 is formed by laminating, in order from the aluminum foil 32 side, a 25 μm PPa (acid-modified polypropylene) layer, a 50 μm PP (polypropylene) layer, and a 25 μm PPa layer, and has a thickness of 100 μm. The sealant film 34 also includes strip-shaped frame portions 32A disposed on each of the four sides of the aluminum foil 32 and protruding portions 34B disposed on both long sides of the aluminum foil 32 so as to protrude from the aluminum foil 32 with a gap therebetween. The protruding portion 34B is disposed so that one end overlaps a part of the frame portion 32A, and the other end protrudes in the shorter direction of the aluminum foil 32.

[0038] Next, as shown in FIG. 2(C), a double-sided laminate film 36 is disposed so as to overlap two adjacent protrusions 34B in the longitudinal direction of the aluminum foil 32. The double-sided laminate film 36 is formed in a rectangular shape, has adhesive applied to both sides, and is disposed so that its longitudinal direction is located inside the adjacent protrusions 34B. Furthermore, as an example, the double-sided laminate film 36 is disposed so that its inner end in the short direction is located inside the protrusions 34B and its outer end is approximately aligned with the outer end of the protrusions 34B. As an example, the double-sided laminate film 36 is formed by laminating, from the aluminum foil 32 side, a 70 μm thick PP layer, a 40 μm thick aluminum layer, and a 70 μm thick PP layer, and has a thickness of 180 μm.

[0039] Next, as shown in FIG. 2(D), two highly molded laminate films 37, each formed in a roughly U-shape with a recess at one end of the rectangular shape, are arranged facing each other with a gap in the longitudinal direction of the aluminum foil 32. The highly molded laminate films 37 are arranged so that the inner edge of the recessed portion is located slightly outward of the inner edge of the frame portion 32A. The highly molded laminate films 37 are also arranged so that the closest opposing edge overlaps the protrusion 34B. For example, the highly molded laminate film 37 is formed by stacking, from the aluminum foil 32 side, a 30 μm PP layer, a 30 μm PPa layer, an 80 μm aluminum layer, a 25 μm Ny (nylon) layer, an approximately 1.5 μm adhesive layer, and a 12 μm PET (polyethylene terephthalate) layer, resulting in a thickness of approximately 178.5 μm.

[0040] In addition, four strip-shaped insulating films 38 are arranged across the boundary between the highly molded laminate film 37 and the sealant film 34 (see FIG. 2(B)). The insulating films 38 are made of the same material as the sealant film 34 described above.

[0041] 2(E), the laminate film thus stacked is embossed along the dotted line indicated by the arrow 39 in an embossing step to form a recess 30A in the center and a flange 30B on the outer periphery. This flange 30B serves as a seal when a pair of exterior bodies 31 are attached with the electrode module 20 enclosed therein.

[0042] Next, a description will be given of the process of assembling the exterior member 30. Fig. 3 is an explanatory view illustrating the process of assembling the exterior member 30 in the secondary battery 10 of Fig. 1. Note that the electrode module 20 shown in Fig. 3(A) has already undergone a reduced pressure sealing process and a self-discharge test.

[0043] As shown in FIG. 3(A), the electrode module 20 is formed in a substantially rectangular parallelepiped shape and includes a liquid filling port frame 12 having a liquid filling port (not shown) through which an electrolyte solution (described later) is filled, and a substrate 14 for detecting the voltage of each bipolar electrode 22 constituting the secondary battery 10. The substrate 14 includes an FPC (Flexible Printed Circuits) board 14A, which is an example of a voltage detection circuit board including a circuit for detecting voltage. Both ends of the FPC board 14A are held by an FPC housing 14B. Also, in FIG. 3, an end current collector 26A is exposed at the center of the vertical end face of the electrode stack 21. The FPC board 14A is subjected to a known sealing process required for sealing with the PP layer on the recess 30A side of the flange 30B of the exterior body 31. In this embodiment, the side on which the substrate 14 is provided will be referred to as the "reference short side," and the side opposite the reference short side will be referred to as the "anti-reference short side."

[0044] Next, as shown in FIG. 3(B), hollow cover members 16 are disposed on the reference short side and the counter-reference short side of the electrode module 20, respectively.

[0045] Next, as shown in Fig. 3(C), a pair of exterior bodies 31 are assembled from both sides of the electrode module 20 on which the cover member 16 is disposed so as to encase the electrode module 20. At this time, a high-friction shim 50 as a metal member is disposed between the electrode module 20 and the exterior body 31. As shown in Figs. 1 and 3, the high-friction shim 50 is disposed between the end collector 26A exposed at the center of the vertical end face of the electrode stack 21 and the aluminum foil 32 in the center of the exterior body 31. Specifically, as an example, the high-friction shim 50 is disposed so as to cover the entire surface of the exposed end collector 26A.

[0046] That is, as shown in Fig. 4, the high-friction shim 50 is disposed between the aluminum foil constituting the end current collector 26A and the aluminum foil 32 included in the exterior body 31. The high-friction shim 50 is made of a metal member having a higher surface hardness and greater surface roughness than the surface of the aluminum foil 32. Specifically, as an example, as shown in Fig. 5, the high-friction shim 50 includes a SUS (stainless steel) foil 52 having polished layers on both surfaces in the thickness direction, and surface-hardened layers 54 provided on the surfaces of the SUS foil 52 on both ends in the thickness direction.

[0047] The polished layer of the SUS foil 52 is formed by blasting the surfaces on both sides in the thickness direction. In the blasting process, the surface roughness of the SUS foil 52 is increased by spraying fine abrasives or the like from a blasting device (not shown). The polished layer is not limited to blasting, and etching, for example, can also be used. Etching can also increase the surface roughness, thereby increasing the frictional force at the contact surface. In addition, the surface-hardened layer 54 is formed, for example, by coating the polished layer of the SUS foil 52 with tungsten, which is generally considered to have high hardness.

[0048] Next, as shown in FIG. 3(D), the flange portions 30B of the pair of exterior bodies 31 are overlapped and bonded together. At this time, as shown in FIG. 3, the flange portions 30B are positioned on the FPC board 14A. In this embodiment, the opposing surfaces of the flange portions 30B of the pair of exterior bodies 31 are made of PP layers. There are no particular limitations on the method for bonding the PP layers together, and known methods can be used. Specifically, for example, hot plate welding, ultrasonic welding, vibration welding, laser welding, or bonding with an adhesive can be used.

[0049] Next, the effects of the secondary battery 10 in the first embodiment will be described.

[0050] Fig. 9 shows a cross-sectional view of a conventional secondary battery 100 corresponding to Fig. 1. In Fig. 9, the same components as those in Fig. 1 are designated by the same reference numerals, and their explanation will be omitted here, with only the different structures being explained in detail.

[0051] In the conventional secondary battery 100, inertial forces (white arrows in FIG. 9) caused by horizontal vibrations or impacts can cause the electrode module 20 to move together with the cover member 16 inside the exterior member 30. If the electrode module 20 moves together with the cover member 16 inside the exterior member 30, there is a possibility that the exterior member 30 will be damaged.

[0052] In the secondary battery 10 of this embodiment, a high-friction shim 50 is disposed between the electrode module 20 and the exterior member 30 that encases the electrode module 20. The high-friction shim 50 is a metal member having a higher surface hardness and a larger surface roughness than the end current collectors 26A (aluminum foils) that constitute the outer surfaces of both ends of the electrode stack 21 of the electrode module 20 in the stacking direction D and the aluminum foil 32 that constitutes the inner surface of the exterior member 30. Therefore, the unevenness on the surface of the high-friction shim 50 penetrates into the end current collectors 26A (aluminum foils) and the aluminum foil 32 of the electrode module 20, respectively, thereby increasing the frictional force at the contact surface with the surface of the high-friction shim 50 compared to when the high-friction shim 50 is not interposed. This suppresses movement of the electrode module 20 within the exterior member 30. Furthermore, because the outer surface of the electrode module 20 is not treated, it does not affect the surface treatment that is typically applied to the electrode module 20.

[0053] Furthermore, in conventional secondary batteries having bipolar electrodes, for example, when the end current collector is made of aluminum, the aluminum surface, which is the outer surface of the end current collector, is subjected to corrosion prevention treatment or treatment to improve sealing strength. Unlike electrode modules having a general electrode laminate, electrode modules having bipolar electrodes require increased static friction resistance between the electrode module and the exterior member while ensuring the current-carrying function of the main surfaces of the end current collector. For example, in an electrode module having bipolar electrodes, treatment to increase static friction resistance on the aluminum surface may have some effect on the treatment applied to the aluminum surface.

[0054] Therefore, in the secondary battery 10 of this embodiment, the electrode stack 21 is configured by stacking a plurality of bipolar electrodes 22 with separators 24 interposed therebetween, and the electrode module 20 includes end current collectors 26A stacked on both ends of the electrode stack 21 in the stacking direction D. Therefore, a high-friction shim 50 disposed between the electrode module 20 and the exterior member 30 can increase the frictional force between the outer surface of the end current collector 26A and the inner surface of the aluminum foil 32 of the exterior member 30 and the surface of the high-friction shim 50. This makes it possible to suppress movement of the electrode module 20 within the exterior member 30 without impeding the current-carrying function of the main plane of the end current collector 26A.

[0055] Furthermore, in the secondary battery 10 of this embodiment, the aluminum foil 32, which is the inner film on the electrode module 20 side of the laminate film that forms the exterior member 30, and the end current collector 26A are made of the same material, namely, aluminum foil. However, because a high-friction shim 50 is provided between the aluminum foil 32 and the end current collector 26A, the unevenness on the surface of the high-friction shim 50 bites into the outer surface of the end current collector 26A and the aluminum foil 32, respectively, thereby increasing the frictional force at the contact surface with the surface of the high-friction shim 50. This makes it possible to suppress movement of the electrode module 20 within the exterior member 30.

[0056] In the secondary battery 10 of this embodiment, the SUS foil 52 constituting the high-friction shim 50 has a polished layer on its surface, which allows for the formation of an uneven, rough surface on the surface of the high-friction shim 50. In addition, the high-friction shim 50 has a surface-hardened layer 54 on the surface of the SUS foil 52, which hardens the uneven surface, making it easier for the unevenness of the high-friction shim 50 to bite into the outer surface of the end current collector 26A and the aluminum foil 32 of the exterior member 30.

[0057] Furthermore, in the secondary battery 10 of this embodiment, a high-friction shim 50 is disposed on the entire outer surface of the exposed end collector 26A, so that movement of the electrode module 20 within the exterior member 30 can be more effectively suppressed.

[0058] 3, the high-friction shim 50 is disposed so as to cover the entire surface of the exposed end current collector 26A, but the present invention is not limited to this. For example, as shown in FIG. 6, the high-friction shim 50 may be formed from four elongated shims 50A, which are arranged in parallel such that the longitudinal direction of the four shims 50A is parallel to the longitudinal direction of the exposed end current collector 26A.

[0059] Also, as shown in FIG. 7, the high-friction shim 50 may be formed from four shims 50B formed in a substantially square shape, and the four shims 50B may be arranged at the four corners of the exposed end collector 26A.

[0060] In this way, by disposing the high-friction shim 50 on a portion of the exposed end current collector 26A, the cost required for the high-friction shim 50 can be reduced.

[0061] (Example) The centerline average roughness Ra and maximum height roughness Rz of each surface of the high-friction shim 50 of the above-described embodiment and a comparative aluminum foil were measured. The centerline average roughness Ra and maximum height roughness Rz correspond to the surface roughness of the present invention. Note that, like the aluminum foil 32 of the exterior member 30 and the aluminum foil constituting the end current collector 26A, the surface of the aluminum foil was carbon-coated. Measurements were performed using a laser microscope equipped with a white light interferometer (Keyence Corporation, VK-X3000) to determine the surface roughness Ra and Rz of each surface. A 10X lens was used, and the measurement area was 1 mm x 1.5 mm. The results are shown in Table 1.

[0062] [Table 1]

[0063] As shown in Table 1, the high-friction shim 50 of this embodiment had larger values ​​than the aluminum foil in both the center line average roughness Ra and the maximum height roughness Rz. In other words, the high-friction shim 50 of this embodiment had a larger surface roughness than the aluminum foil 32 of the exterior member 30 and the aluminum foil constituting the end current collector 26A.

[0064] The static friction coefficient was also measured using the high-friction shim 50 of the above-described embodiment and the aluminum foil used in the surface roughness measurement. Figure 8 is a graph showing the results of the static friction coefficient measurement. As shown in Figure 8, the static friction coefficient μ was measured when aluminum foils were overlapped as a comparative example. The measurement was performed by applying a force to the left and right while the aluminum foils were overlapped, and measuring the maximum static friction force F, which is the friction force just before the aluminum foils began to move. The static friction coefficient μ was calculated from the measured maximum static friction force F and the normal force N, which corresponds to the weight of the aluminum foil, according to the following formula (1). The static friction coefficient μ for the comparative example was 0.280. F = μN (1)

[0065] On the other hand, the static friction coefficient μ was measured for the structure of this embodiment when a high-friction shim 50 was disposed between the aluminum foils. The measurement was performed by stacking the aluminum foil, high-friction shim 50, and aluminum foil in this order, applying force to the left and right sides of the upper and lower aluminum foils, and measuring the maximum static friction force F, which is the friction force just before the aluminum foils began to move. The static friction coefficient μ was calculated based on the measured maximum static friction force F and the normal force N, which corresponds to the weight of the aluminum foil, using the above formula (1). The static friction coefficient μ was 0.666. In other words, the static friction coefficient μ of the structure of this embodiment was approximately 2.4 times higher than that of the comparative example. Therefore, the structure of this embodiment was able to increase the friction force at the contact surface compared to the comparative example.

[0066] [supplementary explanation] In the above-described embodiment, the electrode module 20 includes an electrode stack 21 in which a plurality of bipolar electrodes 22 are stacked, but the present invention is not limited to this, and the electrode module 20 may include a general electrode stack that does not have bipolar electrodes 22, i.e., an electrode stack in which a plurality of cells are stacked. In this case, the metal members disposed between the cases constituting the cells at both ends in the stacking direction and the exterior member 30 are members that have a higher surface hardness and a greater surface roughness than the outer surface of the case and the inner surface of the exterior member.

[0067] Furthermore, in the above-described embodiment, the high-friction shim 50 as a metal member is provided with SUS foil, but the present invention is not limited to this, and may contain a metal other than SUS, or may be provided with, for example, titanium foil instead of SUS foil.

[0068] In the above-described embodiment, the high-friction shim 50 as a metal member has a surface-hardened layer 54 formed by coating tungsten on the polished layer of the SUS foil 52, but the surface-hardened layer 54 is not limited to tungsten. The surface-hardened layer 54 may be made of any material as long as it is made of a material having a surface hardness higher than that of the outer surfaces of both ends in the stacking direction of the electrode stack 21 of the electrode module 20 and the inner surface of the exterior member 30.

[0069] Furthermore, in the above-described embodiment, the aluminum foil 32 forming the inner surface of the laminate film constituting the exterior member 30 and the aluminum foil constituting the end collector 26A are made of the same material, but the present invention is not limited to this and may be made of different materials.

[0070] Furthermore, in the above-described embodiment, the laminate film and sealant film that constitute the exterior member 30 have the above-described configuration, but the present invention is not limited to this, and the materials can be changed as appropriate.

[0071] Furthermore, the configuration of the present disclosure is not limited to the above-described embodiment, and the configuration can be modified as appropriate as long as the problem can be solved. [Explanation of symbols]

[0072] 10 secondary battery, 20, 20A, 20B electrode module, 21 electrode laminate, 22 bipolar electrode, 24 separator, 26 current collector, 26A end current collector, 27 positive electrode, 28 negative electrode, 30 exterior member, 50 high-friction shim (metal member), 52 SUS foil (metal foil), 54 hardened surface layer

Claims

1. an electrode module including an electrode stack in which a plurality of positive electrode layers and negative electrode layers are stacked with separators interposed therebetween; an exterior member that encases the electrode module; a metal member disposed between the electrode module and the exterior member, the metal member having a surface hardness higher than that of outer surfaces of both ends of the electrode stack of the electrode module in the stacking direction and a surface roughness larger than that of an inner surface of the exterior member; A secondary battery having the above structure.

2. the electrode stack is configured by stacking a plurality of bipolar electrodes, each of which has the positive electrode layer formed on one surface of a current collector and the negative electrode layer formed on the other surface, with the separator interposed therebetween; The secondary battery according to claim 1 , wherein the electrode module includes end current collectors stacked on both ends of the electrode stack in the stacking direction.

3. The secondary battery according to claim 2 , wherein the metal member is disposed between at least a part of the end current collector and the exterior member.

4. the exterior member is a laminate film formed by overlapping film materials, 2. The secondary battery according to claim 1, wherein an inner film of the laminate film on the electrode module side and outer surfaces of both ends in the stacking direction of the electrode stack are made of the same material.

5. The metal member is a metal foil having a polished layer on its surface; 2. The secondary battery according to claim 1, further comprising a surface hardening layer provided on the surface of each of both ends of the metal foil in the thickness direction.

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